How do I select strips in the Video Sequence Editor?
you can use some of the same selection tools that are used throughout blender. 

Pressing A will select all.

WithByou can do box select and draw a rectangle around the things you want to select.

You can just click-select individual strips or press shift and click to add to the current selection.

Clicking CtrlI will inverse the selection.

CtrlNumpad + and CtrlNumpad - will select more or less.

Also if you look at the menu there are a lot more options: